Our unique resource of extended pedigrees with autism spectrum disorder (ASD) will allow us to make important contributions to genetic studies of ASD. We will sequence family members from the most informative pedigrees to study genetic variation contributing to ASD and related phenotypes. We will work to discover new variation, and also use the resource to characterize variants in conjunction with existing whole exome data available through our collaborations. We will test findings in up to 10 other families available from the Autism Genome Project (AGP) network of collaborators. We will also make the resource available to the broader scientific community. Extended families offer an excellent opportunity to identify and study genetic variation, giving a complementary approach to ongoing studies of simplex and small multiplex families. The current collection of families represents some of the largest pedigrees with ASD in the world. We have already detected significant linkage evidence in some of these families with clinical diagnosis and also with related phenotypes, including gender; Full Scale IQ; discrepancy between verbal and nonverbal IQ; language delay, Insistence on Sameness, Repetitive Sensory-Motor Actions (RSMA), overall clinical severity, and regressive onset (all derived from the ADI); head circumference; and the Broader Autism Phenotype. Sequence data in these extended families will result in highly accurate and extensive genetic information. We will identify familial variation in these data, and predict potentially deleterious variants using new informatics approaches. We will refine information about risk by comparing to ongoing sequence projects. We will also use the ongoing sequence projects to help prioritize the familial variant discovery, and choose the best for replication efforts in other AGP families. Finally, we will investigate sequence variants found by simplex/small family sequencing to determine specificity and penetrance in our extended families. Our proposed project will benefit from the continued collaboration of excellent molecular, analytic, and clinical expertise in the Autism Genome Project to enable the most effective use of this unique resource.